Last year we reported that the endogenous cat virus, RD-114, was able to productively infect 13 of 13 cat embryonic cell lines tested. Studies with additional embryos have served to extend this observation. Further biological studies have revealed the presence of two distinct sub-types of RD-114 virus. Additionally, cat embryo cells can be characterized as "permissive" or "restrictive" based on results obtained with the two virus sub-types.